There are dozens of patents for different configurations mounted on the flat end of a large truck trailer to decrease the air drag of the moving trailer. The main object always is to fill in the low pressure region in the vicinity of the rear vertical surface. Actually, a portion of the pressure drop at the rear surface is contributed to by the organization of the air flow streaming rearward, i.e., following the truck end. The flows from the sides, the top and the bottom inward tend to create a vortice in the wake region of the trailer. This strengthens the suction drag (low pressure) at the rear compared to a wake without the vortices
Each of the many patented inventions cover ways to influence air motion at the rear of the trailer. Our invention specifically obviates the vortices formation. It does this by means of air foils of minimum complexity.
The invention is essentially a truncated, four-sided, hollow pyramid with the base closely matching the perimeter of the rear vertical surface of the trailer. The pyramid is divided internally, vertically into two chambers with vertical walls that are curved, in effect, to form two adjacent xe2x80x9cUxe2x80x9d shaped cavities with the open ends facing rearward. This shape facilitates the development of rear air flow forward within the pyramid from the vertical edges and into each xe2x80x9cUxe2x80x9d shape including an 180 degree turn rearward, behind and away from the trailer in non-rotating flow retreating behind the moving trailer. The depth of the xe2x80x9cUxe2x80x9d shaped cavities can be less than the overall height of the truncated pyramid. In another form of the invention each xe2x80x9cUxe2x80x9d has a vertical splitter wall extending from the rear of the apparatus forward into each xe2x80x9cUxe2x80x9d approximately three-fourths of the depth of the xe2x80x9cUxe2x80x9d in order to reduce air entrainment between the entering and exiting streams of air in each cavity.